Solvent fractionation of stearincontaining oils



H. J. FASSINO Dec. 27, 1955 SOLVENT FRACTIONATION OF' STEARIN-CONTAINING OILS Filed June 18, 1954 mm2/OP INVENTOR.

HERBERT J. PASS NO By ATTORNEYS SOLVENT FACTIONATION F STEARIN- CONTAINING OILS Herbert J. Passino, Englewood, N. J., assigner to The M. W. Kellogg Company, a corporation of Delaware Application June 18, 1954, Serial No. 437,633

` claims. (ci. 167-81) This invention relates to an improved method for the treatment of natural or fatty oils such as animal oils, tish oils, and vegetable oils for separating from such oils one or more fractions in which a particular desired component is concentrated. More particularly, this invention relates to methods for treating fatty oils in which the treatment thereof is carried out in the presence of a selective solvent whose miscibility with the oil decreases with increasing temperature.

This application is a continuation-in-part of my copending application S. N. 146,229, iled February 25, 1950, as a continuation-in-part of then co-pending application S. N. 668,667, filed May l0, 1946, andboth now abandoned.

lt is known that a natural or fatty oil can be treated with a selective solvent such as a liquied normally gaseous hydrocarbon or the like under such conditions that certain desired components thereof can be recovered very efficiently and in avery pure state. According to such method the oil is preferably treated with the solvent in a counter-current extraction zone under such conditions of temperature and pressure that the solvent is maintained in a liquied state and increases in temperature will cause decreases in the miscibility of certain components of the oil and the solvent. A method of this type for treating natural and fatty oils is described in U. S. Letters Patent 2,394,968, issued to Leo J. Van Orden on February 12, 1946.

One of the principal applications of the process according to the present invention, is the treatment of fatty oils to separate a component therefrom which exists only in relatively small proportions such as the phosphatides in soybean oil and the tocopherols in cottonseed oil and soybean oil. For example, also certain natural oils contain varying amounts of vitamins which it is desired to concentrate. This invention may also be applied to the separation of other desired components from natural oils, but since it is particularly applicable to the production of vitamin concentrates the process will be described in detail by reference to the treatment of those fatty oils which contain vitamins tov a greater extent than in other fatty oils. Such oils are tish oils, i. e., fish liver oils and lish body oils.

The charge oil may be treated to produce vitamin concentrates at relatively low temperatures by means of solvents for such oils or portions thereof whose miscibility with the oil decreases with increasing temperature. In such cases, the range of operating conditions of temperature and pressure is frequently fairly close to the critical, because when the temperature is increased, the density of the solvent is decreased to such an extent as to cause the solvent power for the oil to be decreased. Such solvents are normally gaseous and must be used under such conditions of pressure that the required degree of solvency for the vitamin oil is obtained. The solvent in the liquid state and charge oil are contacted preferably in a counter-current extraction zone under conditions of temperature and pressure so as to cause United States Patent() "ice the formation of two homogeneous mixtures of the solvent and oil which constitute immiscible liquid phases of differing densities. The upper or lighter phase consists principally of the solvent and the desired portion of the oil, while the lower or heavy phase is made up of the remainder of the oil and a small portion of the solvent. In the treatment of various fish oils for the recovery of concentrates containing vitamin A and/or vitamin D, it has been found that they are concentrated in the lower density phase.

The solvents which may be used for the present process must exhibit the characteristics of having decreased solvent power for various components of the oil as the temperature is increased. In addition, the range of temperatures employed must be substantially below those temperatures at which any thermal decomposition or chemical reaction occurs in the charge oil. Preferably the solvent should have a critical temperature Well below the decomposition temperature of the charge oil, i. e., not substantially higher than 450 F., and the miscibility of the oil and solvent should decrease with increases in the temperature in the range between that temperature at which there is substantially complete miscibility of the solvent and oil, i. e., below about 50 below the critical temperature to a higher temperature not substantially greater than the critical temperature of the solvent. At the higher temperature the oil and solvent are substantially immiscible. The low molecular weight hydrocarbons are particularly suitable for use in the present process since they exhibit the above necessary characteristics. The low molecular weight paratln hydrocarbons are especially useful since they are inert to substantially all components of the charge oil. The low boiling normally gaseous and normally liquid parain hydrocarbons such as methane, ethane, propane, the butanes and the pentanes are, therefore, preferred as solvents, but it has also been found that the corresponding olefin hydrocarbons may be used with satisfactory results and these latter compounds are, therefore, not excluded. Since propane exhibits all of the desired characteristics to a higher degree than some of the other solvents mentioned, it is the preferred solvent for the present process. Furthermore, mixtures of any two or more of the above mentioned hydrocarbon solvents may be used as well as the relatively pure compounds. In addition to those solvents previously mentioned, other solvents having relatively low critical temperatures may also be employedsuch as ammonia and the halogenated hydrocarbons such as dichlorodifluoromethane.

According to the present process the solvent and the desired portion of the 4oil is taken overhead from the countercurrent extraction zone while the less desirable portion of the oil and a minor amount of the solvent is removed from the bottom of said zone. If desired, intermediate fractions may also be recovered. In addition to the desired components to be found in the overhead fraction, various undesirable components will also be found in this fraction.

ln the case of vitamin oils and vitamin concentrates, the principal undesired component found in the overhead fraction is stearin as well as other relatively high melt-- ing point substances. The use of the term stearin in this specification includes not only the glycerides, such as glyceryl tristearate, but also occasionally a mixture of fatty acids such as stearic and palmitic acids. In addition to these substances various other relatively high melting point substances are sometimes present, such as the sterols.

The presence of the stearin in the overhead fraction containing the vitamins or other desired components is undesirable for at least two reasons. A commercial vitamin product in which the vitamins are dissolved in oil must amavo? meet certain standards at low temperatures due to the precipitation of the stearin. Furthermore, the presence of stearin is undesirable since it decreases the concentration of the vitamins in the final product.

However, the stearin is itself a solvent for vitamins and some other components which it is desirable to extract from fatty oils by applicants method. Thus, a stearinpropane mixture may be a better solvent for high recovery of vitamins, or other substances, than the same quantity of propane alone, in spite of the fact that stearin is undesirable in the tinal product.

Ordinarily, the stearin is removed from the overhead fraction after the solvent has been removed, by winterizing or chilling the oil so as to crystallize the stearin and then filtering the stearin from the oil. This oil generally meets the tests for cloud formation at low temperatures. However, an appreciable amount of oil is lost to the stearin cake along with those vitamins dissolved in the occluded oil. Normally the stearin cake is disposed of as a vitamin product of low concentration and occasionally the stearin cake is washed with additional solvent in an effort to recover as much of the occluded oil and vitamins as possible.

According to the present invention substantially all of the oil which has heretofore been lost to the stearin cake is recoverable in a simple, efficient and economical man ner. It has been found that the stearin cake may be returned to the fractionation or counter-current extraction zone where it will be dissolved and stripped of the occluded oil.

When this process is applied to vitamin-containing oils such as ish liver oils or fish body oils, only a very small overhead fraction is obtained. This fraction consists of from about 1% to about 10% of the original oil, but nevertheless, contains practically all of the vitamins. In addition, this overhead fraction contains other unsaponifiable materials such as the sterols and a proportion of the saponiable materials, i. e., the stearin. ln a representative fractionation, a crude cod-liver oil containing approximately 11% stearin was fractionated with propane under-such conditions that a 1% overhead fraction was obtained. This overhead fraction contained 4.5% of the original stearin (or 0.5% based on original oil charge) which constituted 50% of the overhead fraction. It is therefore clear that while approximately 95% of the stearin is removed with the bottoms from the tower, that portion which accompanies vthe overhead fraction constitutes a major proportion of that fraction. When the overhead fraction is chilled to crystallize practically all of the stearin contained therein and is then filtered, the stearin cake which contains some yof the vitamin oil is returned to the extraction zone either as a slurry or in propane solution where it will be contacted by the charge oil and propane solvent. The filtrate which contains the vitamins may also contain very small amounts of stearin which were not removed by the chilling and filtering operations. The ratio of propane to oil in the tower is ad# justed so that the relative proportions of stearin going overhead and being removed from the bottom of the zone will remain substantially the same even though the amount of stearin in the column is slightly greater than the amount contained in the charge oil. In this manner, the amount of stearin contained in the extraction zone will increase due to the introduction of the stearin cake. This build-up of stearin in the extraction zone will continue until the amount of stearin being withdrawn from the bottom of the extraction zone approaches the amount of stearin present in the charge oil. Since approximately 95% of the stearin present in the zone is always withdrawn from the bottom of the zone, the build-up of stearin will be very slight. In the case of the example given above where the charge oil contained 11% stearin, the initial overhead contained 0.5% stearin (based on charge oil) and the bottoms contained 10.5% stearin, under nal equilibrium conditions the overhead will contain slightly more than 0.5% where- 4 as the bottoms will contain practically 11.00% stearin. Since the total stearin entering the tower in the charge oil equals 11%, it is clear that no further build-up of stearin will occur in the zone.

There is danger of a build-up of relatively soluble, high melting point fatty acids in the tower and in the overhead fraction, however, if these fatty acids have not been climi nated from the crude oil prior to its introduction into the extraction zone. Less soluble fatty acids cause no problem since they go out with the bottoms fraction. Of the more soluble fatty acids, those which have a low melting point do not present a problem since they are not precipitated with the stearin cake but are retained in the tiltrate and are eventually eliminated when the vitamin concentrate or other product is neutralized. But those fatty acids which are both soluble enough to get into the overhead and have a suficiently high melting point to be precipitated with the stearins introduce a special problem since they return to the extraction zone with the stearin recycle and reconcentrate into the overhead phase. With the passage of time, the percentage of these recirculating fatty acids increases to such a degree that they may actually comprise an excessive percentage of the overhead fraction and may displace desired product material into the bottom fraction. Of course, the problem can be overcome by sufficiently neutralizing the crude oil before introducing it into the fractionation zone; but if this is not desirable. all or a part of the overhead fraction, or of the stearin recycle portion of the overhead fraction, may be neutralized to prevent the build-up of an undesirable quantity of fatty acids within the system.

The accompanying drawing illustrates a flow sheet of a system for treating a fatty oil according to the present invention. The drawing illustrates all of the essential features of the system but does not include various mechanical details such as valves and the like, nor does it include those elements of the system, such as reux lines and the like which are well-known to those skilled in the art.

The crude fatty oil feed is introduced through line 11 and caustic through line 12 to line 1.3, which enters the neutralizer tower 14. It is desirable to remove a large proportion of the fatty acids and some glycerides from the oil'and this is generally accomplished by neutralizing the acids with caustic to form soaps, This step may be carried out before or after the propane fractionation step. The Asoaps are removed from the bottom of the tower 14 through line 15. The overhead from tower 14 is passed through line 16, pump 17 and heat exchanger 18 for preheating the fatty oil to the proper temperature. The oil is then introduced into an extraction or fractionating tower near the midpoint thereof through line 18a, and propane is introduced from storage tank 20 through line 21, pump 22 and heat exchanger 23 to a point near the bottom of tower 19. lf desired, the oil may be introduced Ato' tower I9, near the top thereof through a line 24 shown in dotted lines. When the oil is introduced through line 18a, the lower part of tower 19 will operate as an absorption zone while the upper part of the tower will serve as a rectification zone as will be described more fully hereinafter. As the propane rises through the tower and the fatty oil descends therethrough, a countercurrent extraction of the oil is effected and various components of the oil which are insoluble or immiscible with the propane such as saponifiable material including various glyceri'des and the like will ow to the bottom of the tower, where they are withdrawn through line 25. An overhead fraction is withdrawn through line 26 and consists largely of a propane solution of the unsaponfiable materials including the vitamins. The overhead also includes a portion of the stearin as well. This overhead fraction is then passed through a chiller or cooler 27 to a tilter drum 28 via line 28a where the stearin and other relatively high melting point substances which have been crystallized by the chilling operation are separated from amener the oily material. Any type of filter may be used for this operation such as a disk-type filter, a drum-type lter or in many cases a conventional settler may be used. The ilter cake is returned through line 29 to the tower 19 and may be introduced at any one of a number of points intermediate the top and bottom of the tower as illustrated by lines containing valves 29a, 29b, and 29C. The transfer of the stearin cake may be accomplished by intermittently introducing additional propane through line 30 to the filter 28 so as to form a slurry or solution with the lter cake after the ltrate has been removed, or the stearin cake may be heated, for example, by warm propane to melt the stearin for returning it to the tower in fluid form.

lf the crude oil contains relatively soluble fatty acids which have a high melting point and which have not been eliminated by neutralization in neutralizer tower 14, then it is usually necessary to treat at least a part of the overhead fraction to remove them. Since it is also customary to neutralize the product, it may be desirable to neutralize the entire overhead fraction for the two purposes of eliminating high melting point fatty acids from the stearin recycle and of eliminating low melting point fatty acids from the product. To this end, the overhead fraction may be passed through neutralizer 31 by diverting it from line 26 to line 31a. Neutralizer 31 is a vessel in which the overhead fraction is contacted with aqueous caustic solution introduced at 31h; soaps are settled and withdrawn from line 31C. However, in many cases it may be preferred to do only enough neutralizing of the overhead to remove sufficient fatty acids so that the process operates satisfactorily. In this event, only part of the overhead fraction may be diverted through neutralizer 31 or overhead fraction material may be diverted to neutralizer 31 only intermittently, when, after a period of continuous operation without overhead fraction neutralization, the fatty acid content has become excessive; or a neutralizer 32, similar to neutralizer 31, may be employed for continuously or intermittently neutralizing all or part of the stearin recycle passing through line 29.

Neutralizers 31 and 32 may be supplemented or replaced by diverting all or part of the stearin recycle in line 29 through line 33 to crude oil inlet line 11. Thus, the stearin recycle or that portion of it which is diverted through line 33 is mingled with the crude oil and contacted with caustic in neutralizer tower 14 before returning to fractionating tower 19.

The filtrate from filter 28 is passed through line 34 to a flash drum 35 where most of the propane is recovered and returned through lines 36 and 37 to storage tank 20. The oil material is withdrawn from the bottom of drum 35 and is passed through line 38 to a steam stripper 39. The stripper removes further amounts of propane which pass through line 40 to a condenser 41 where water is separated therefrom. The propane is then returned through line 42 to line 37 and the storage tank 20. A substantially destearinized product is recovered from the bottom of stripper 39 through line 43.

The bottoms from fractionator 19 are passed through line 25 to flash drum 44 from which propane is recovered and returned to the system through line 45. The bottoms from flash drum 44 which consists of stearin and other saponiiables are passed through line 46 to a steam stripper 47 for removing additional quantities of propane. The bottoms from stripper 47 are withdrawn through line 48 for further disposition and the overhead passes through condenser 49 to remove water.

When charge oil is introduced through line 18a to the mid-point of tower 19, a maximum temperature is maintained at the top of the tower and a minimum temperature at the bottom of the tower. The bottom temperature is conveniently controlled by introducing propane through line 21 at the desired temperature. The oil which is introduced through line 18a may be heated to the same emperature so that the temperature is substantially uniform between the oil and propane charge points, or if desired, the oil may have a higher temperature than the propane so that there will be a temperature gradient between the charge points.

The lower portion of the tower 19 below the oil charge point functions primarily as an absorption zone in which the components of the oil which are not absorbed by the upwardly flowing propane flow downwardly through the tower by reason of their greater gravity. As the oil ows downwardly it contacts propane which is less saturated with respect to the oil so that more and more of the oil is absorbed in the propane phase. The unabsorbed oil which contains propane in solution therewith, is collected atthe bottom of tower 19 and is withdrawn through line 25. The interface between the propane phase and the oil phase may be maintained above or below the propane charge point. However, in order to obtain a stripping effect the interface may be located above the propane charge point.

As the propane phase rises upwardly through the tower above the oil charge point, it is progressively heated to higher temperatures by means of heating coils not shown. As the propane phase moves upwardly through this portion of the tower and is heated to a relatively higher temperature, the less soluble portions of the oil dissolved in the propane are precipitated as a separate and heavier phase containing substantially less propane than the propane phase. The precipitated oil ows downwardly from the point of precipitation in counter-current contact with the upwardly flowing propane phase and passes from a higher temperature to a zone of lower temperature at which the capacity of the propane phase to absorb the oil is greater than that at the temperature at which the precipitated oil was precipitated. Therefore, the propane phase tends to reabsorb oil precipitated from the propane phase at a higher temperature and at a higher point in tower 19. It will be seen, therefore, that a highly etiicient rectification of the vitamin oil is obtained whereby eicient separation of that portion of the oil containing the vitamins is effected. As stated before, the vitamins are concentrated in the propane phase which is withdrawn from the top of tower 19 through line 26.

The maximum temperature generally employed at the top of the tower may be higher than the critical temperature of the propane or other solvent, but it is preferred ordinarily to operate at temperatures below the critical temperature and falling within the range of temperatures between the critical temperature and 30 F. below the critical temperature. Within this range of temperatures the lower temperatures are employed at the top of the tower when it is desired to obtain an overhead fraction containing a relatively greater proportion of the oil feed Whereas higher temperatures are employed when only a small overhead fraction is desired. When relatively high ratios of propane to oil are used, the proportion of oil absorbed is greater and the maximum temperature at the top of the tower must be established with respect to the solvent to oil ratio when a particular fraction of the oil is desired.

The temperature at the bottom of tower 19 must, of course, be above the temperature at which complete miscibility of the oil and solvent occur. The preferred bottom temperatures are generally maintained at LO-50 F. or more below the critical temperature of the solvent. When propane is employed as the solvent in the concentration of sh oils containing vitamins A and/or D, the temperature at the top of the tower may be between -200" F. and the bottom temperature at 160 to 180 F.'

The pressure employed in the extraction tower 19 is maintained suiciently above the vapor pressure of the v solvent to permit substantial variation in the tower pressure without reducing it below the Vapor pressure of the solvent. A maximum operating pressure of 50 pounds per square inch higher than the vapor pressure of the solvent is generally sufficiently high since adjustments of 10 to 15 pounds in the operating pressure arev usually suicient to counteract whatever temperature variations may occur in the operation of the tower.

For a fuller understanding of the present invention, a specific example will be described in connection with the operation shown on the accompanying drawing. The crude oil employed is a cod liver oil having the following properties:

Table Vitamin A potency:

Whole oil 2120 units.

Unsaponiable oil 1945 units. Color- Gardner 6+. Color-Lovibond Y-6.5R. Free fatty acids (as oleic) percent 0.77. Unsaponiiable oil, Weight percent 1.4. Saponification No 185. Iodine No. (Wijs) 162. Cloud point, F +55. Pour point, F +15. Specific gravity (/60 F.) 0.925.

The cod liver oil described above is charged to the neutralization tower 14 along with 3 normal aqueous potassium hydroxide via 'line 12 at the relative rate, on a weight basis, of 38 parts of caustic per hundred parts of cod liver oil. The tower 14 is maintained at atrnospheric pressure and about F. As previously indicated, the resultant soaps are discharged from the bottom of the tower via line 15, whereas the neutralized oil Y is charged to fractionating tower 1.9 via line 13a. Propane is fed to the bottom of tower 19 by means of line 21 at a rate sufficient to provide a volumetric ratio of 50:1 of propane to oil. The propane is introduced at a temperature of 170 F. The temperature at the bottom of the tower is 171 F. and the top tower temperature is 199 F. At the point where neutralized cod liver oil is fed to the tower, the temperature is about 187 F. The tower pressure is 675 p. s. i. g. The neutralized cod liver oil has a residence time of 25 minutes in tower i9, resulting in a vitamin concentrate fraction dissolved in propane to be discharged overhead from the tower via line 26. The oil portion of the overhead product constitutes about 1.105% by weight of the total feed and it contains 0.4% by weight of stearin, basis total feed.

The Overhead product is chilled to a temperature of --40 F., whereupon the stearin is solidified. This solidilied stearin is separated by iltra'tion, and it is recycled to the fractionating tower via line 2917. The stearin recycle contains 0.37% by weight of stearin, basis total feed, and 15% of the vitamin concentrate in the overhead prodnct. The remaining filtrate is subjected to a flashing operation in flash drum 35 for the removal of propane, and the vitamin concentrate which is discharged therefrom is further processed for the removal of propane in stripper 39. rihe vitamin product leaving tower 39 through line 43 constitutes 0.63% by weight of the total feed, and about 0.3% by weight, basis total feed, is stearin. This vitamin concentrate has a potency of 339,200 units. The undissolved oil along with the bulk of the stearin which is not yielded with the vitamin concentrate in line 43 is discharged from the bottom of the fractionating tower l? by means of line 25. This stream is further processed for the removal of propane, and subequently, the remaining oil is yielded from the bottom of stripper 47 by means of line 4S.

ln another example of the present invention, the process may be carried out extactly as just described, except that the circulation of fatty acids in the system may be prevented by neutralizing the vitamin concentrate extract fraction withdrawn from the top of tower 19. ln this variation, about 600 parts of three normal aqueous potassium hydroxide should be employed for every parts of extract oil on a weight basis. if neutralization is done at this stage, the preliminary neutralization in tower 14- is not always necessary; it may or may not be employed, depending on the quality of the crude oil and on economic considerations of cost versus product quality.

A third example involves neutralizing the stearin recycle, either warmed up or slurried. The stearin recycle may be neutralized continuously or intermittently or only part of it need be passed through neutralization. Here again, 600 parts by weight of three normal aqueous potassiumrhydroxide should be employed for each 100 parts of stearin recycle. Neutralization at this point will prevent internal circulation of fatty acids regardless of whether or not the crude oil is subjected to preliminary neutralization. However, neutralization at this stage does not provide for any neutralization of the vitamin product itself. Preliminary neutralization of the crude oil or subsequent neutralization of vitamin filtrate may be desired in addition to neutralization of recycled stearin, in order to insure a fatty acid-free vitamin product.

lt will be understood, of course, that neutralization may be omitted entirely if the crude oil is sufficiently neutral or if the advantages of neutralization are economically less important than its cost.

The present invention has been described with particular reference to a speciiic embodiment thereof. However, it will be recognized that I do not intend to be limited by this description but rather that the scope of the present invention should be deiined by the appended claims.

l claim:

l. In a method of treating a stearin-containing oil to separate said oil into at least two components in which said oil is contacted with a low boiling solvent having a critical temperature not substantially greater than 450 F. at a temperature at which the solubility of the oil in the solvent decreases with rising temperature in an extraction zone and in which an overhead fraction containing a portion of the stearin and other relatively high melting substances is withdrawn from said zone, the improvement comprising cooling said overhead fraction to crystallize said stearin and said other substances, removing the crystallized material from said fraction, returning said crystallized material to said extraction zone and recovering a stearin-free oil .as a product of the process.

2. A method of treating fatty oils containing stearin a's claimed in claim 1 wherein at least part of the fatty acid content of the overhead fraction is eliminated by treat ing said overhead 'fraction with an alkali prior to said cooling step.

' 3. A method as claimed in claim l, in which the solvent comprises a liquified normally gaseous hydrocarbon.

4. A method of treating fatty oils containing stearin as claimed in claim l, wherein the solvent is propane.

5. In a method of treating a vitamin and stearin containing fish oil to separate therefrom a portion containing vitamins in higher concentration than said oil, in which said oil is contacted with a low boiling solvent having a critical temperature at which the solubility of the oil in the solventdecreases with rising temperature in a continuous counter-current extraction zone and in which an overhead fraction containinfr vitamins, a portion of the stearin and other relatively high melting substances is withdrawn from said zone, the improvement comprising cooling said overhead fraction to crystallize said stearin and said other relatively high melting substances, filtering the crystallized material from said fraction, treating at least a part of said crystallized material with an alkali to reduce the fatty acid content thereof, returning said crystallized material to said continuous counter-current .extraction zone, and recovering a vitamin concentrate from the filtrate withdrawn from said filtering step.

6. A method of treating fatty oils containing stearin to separate said oils into at least two components having different characteristics which comprises contacting said oils with a liquited normally gaseous hydrocarbon at a temperature at which the solubility of the oil in sail hydrocarbon decreases with rising temperature in a continuous counter-current extraction zone, withdrawing an overhead fraction from said zone containing a portion of said stearin and other relatively high melting substances, cooling said overhead fraction to crystallize said stearin and said other substances, filtering the crystallized material from said fraction, adding additional liquiiied normally gaseous hydrocarbon to said crystallized material to form a slurry thereof, returning said slurry to the upper portion of said extraction zone and recovering a stearinfree oil as a product of the process.

7. A method of treating fatty oils containing stearin to separate said oils into at least two components having different characteristics which comprises introducing said oils into an extraction zone near the mid-point thereof, introducing a low-boiling solvent whose critical temperature is not substantially higher than 450 F. into said extraction zone near the bottom thereof, maintaining conditions within said extraction zone such that said solvent will remain in the liquid condition and at a temperature at which the solubility of the oil in the solvent decreases with rising temperature, withdrawing an overhead fraction from said zone containing oil and a portion of said stearin and other relatively high melting substances, cooling said overhead fraction to produce a solids phase including at least a portion of said stearin and said other substances, removing the solids phase from the oil phase, returning said solids phase to said extraction zone at a point above the mid-point thereof and recovering a stearin-free oil as a product of the process. v

8. A method for continuously fractionating a fatty oil containing stearin and fatty acids with a low-boiling solvent whose critical temperature is not substantially higher than 450 F. to separate said crude oil into at least two components having different characteristics, which method includes the steps of: introducing said fatty oil into a fractionating zone and continuously counter-currently contacting said oil with said solvent while maintaining conditions within said fractionation zone such that said solvent will remain in a liquid condition and in a temperature range in which the solubility of the oil in the solvent decreases with increasing temperature; withdrawing from said zone an overhead fraction containing extract oil and a portion of said stearin, and other relatively high melting point substances; cooling said overhead fraction to separate it into an oil phase containing extract oil, and a solids phase containing at least a portion of said stearin, said fatty acids, and said other substances; removing the solids phase from the oil phase; returning said solids phase containing stearin to said fractionating zone in a crude oil mixture, and recovering an extract oil from said oil phase.

9. A method for preparing a vitamin concentrate from a neutralized fish oil containing some vitamins, stearin and fatty acids by continuously fractionating said oil with a normally gaseous hydrocarbon solvent, which method includes the steps of: continuously introducing said neutralized sh oil into a fractionating zone and countercurrently contacting said oil with said solvent while maintaining conditions within said fractionation zone such that said solvent will remain in a liquid condition and in a temperature range in which the solubility of the oil in the solvent decreases with increasing temperature; withdrawing from said zone an overhead fraction containing a concentrate of vitamins and a portion of said stearin and fatty acids; cooling said overhead fraction to separate it into a lower density phase, containing vitamin concentrate, and a higher density phase, containing stearin, and occludcd vitamins; removing the higher density phase from the lower density phase, diluting said higher density phase with propane and introducing it into said fractionation zone; and recovering a vitamin concentrate from said lower density phase.

10. A method as claimed in claim 9 in which said higher density phase is slurried with propane and then mixed with said sh oil feed to said fractionation zone.

References Cited in the tile of this patent UNITED STATES PATENTS 2,288,441 Ewing June 30, 1942 2,389,955 Buxton Nov. 27, 1945 2,394,968 Van Orden Feb. 12, 1946 2,499,991 Dickinson Mar. 7, 1950 2,505,338 Palmer Apr. 25, 1950 

1. IN A METHOD OF TREATING A STEARIN-CONTAINING OIL TO SEPARATE SAID OIL INTO AT LEAST TWO COMPONENTS IN WHICH SAID OIL IS CONTACTED WITH A LOW BOILING SOLVENT HAVING A CRITICAL TEMPERATURE NOT SUBSTANTIALLY GREATER THAN 450* F. AT A TEMPERATURE AT WHICH THE SOLUBILITY OF THE OIL IN THE SOLVENT DECREASES WITH RISING TEMPERATURE IN AN EXTRACTION ZONE AND IN WHICH AN OVERHEAD FRACTION CONTAINING A PORTION OF THE STEARIN AND OTHER RELATIVELY HIGH MELTING SUBSTANCES IS WITHDRAWN FROM SAID ZONE, THE IMPROVEMENT COMPRISING COOLING SAID OVERHEAD FRACTION TO CRYSTALLIZE SAID STEARIN AND SAID OTHER SUBSTANCES, REMOVING THE CRYS- 